1. Field of the Invention
This invention relates to a composition and method useful in removing paraffin and paraffin-like materials from oilfield equipment and the associated environment, such as may occur on the face of the producing formation, in the pump, in the casing or the tubing of the well and in oil flowlines and pipelines, tank batteries, tank farms and the like.
In many oilfields, particularly in those which produce fairly waxy crudes, production is limited as a result of the deposition of paraffin and paraffin-like deposits in the formation as well as in the oil production, transportation and storage equipment. It is not uncommon that the flow of oil from a well is completely stopped due to paraffin deposition. Further, deposition of paraffin and paraffin-like materials in pipelines results in increased pumping and maintenance costs.
The need for removal of paraffin deposits from well production transportation and storage equipment is obvious. In some areas, wells decline in productivity at a more or less rapid rate because of the deposition of such deposits on the face of the producing formation. In other cases, the decline is sufficiently rapid that the wells must be serviced in some manner at a frequency ranging from several days to several weeks. In other instances, the paraffin deposition is at such a slow rate that servicing at long intervals is sufficient to maintain the well at a satisfactory level of production. The same is true of the various conduits in which the oil travels from the well to the refinery. The capacity of a conduit or circuit of cross-section is reduced greatly by paraffin deposition, usually well beyond the reduction expected from the ratio of effective cross-sectional area of the conduit and the fouled conduit. Where paraffin deposits occur on formation walls, well productivity may fall substantially to zero, especially in low-pressure fields. Pipe capacities are frequently reduced to a small fraction of their capacities when cleaned. Ultimately, such pipes may be found completely clogged by paraffinic deposits.
Various techniques have been employed for the removal of paraffin deposits from oil-producing formations and wells penetrating such formations. These techniques include the use of mechanical and heating devices, explosives and solvents. Various solvents which have been used to dissolve paraffins include, benzene, xylene, toluene, gasoline, carbon tetrachloride and carbon disulfide.
One of the most effective solvents for paraffins of widely differing compositions is carbon disulfide. The use of carbon disulfide is difficult and hazardous, however, since it is extremely toxic and flammable, having a low flashpoint (-30.degree. C.) and auto-ignition temperature (approximately 102.degree. C.).
2. Description of the Prior Art
U.S. Pat. No. 3,718,586 describes a solvent mixture of liquified petroleum gas (a mixture of lower alkanes) and a very small amount of a liquid aromatic hydrocarbon. In Column 2, lines 39-43 of this patent, it is taught that the lower alkane and the liquid aromatic hydrocarbon are present in the volume ratio of 100:1 to about 500:1 and ideally present in a volume ratio of between about 250:1.
U.S. Pat. No. 3,241,614 describes a process of removing hydrocarbon accumulations by contacting the hydrocarbons with a liquid mixture of a solvent and a surfactant. Various hydrocarbon solvents are mentioned, as is carbon disulfide.
U.S. Pat. No. 3,375,192 describes a mixture for cleaning oil wells which is composed of carbon disulfide and pentane.
U.S. Pat. No. 3,402,770 discloses a single-base solvent which is used to dissolve flow-restricting materials in oil wet equipment. The solvent is a solution comprising an organic solvent for oil and asphalt and a liquid having mutual solubility for oil and water. Carbon disulfide is disclosed as the preferred organic solvent for oil and asphalt.
U.S. Pat. No. 2,358,655 discloses a method of removing paraffin from oil well tubing by the use of a solvent emulsion which consists essentially of a wax solvent, a petroleum distillate and water. Carbon tetrachloride and carbon disulfide are disclosed as examples of wax solvents.
U.S. Pat. No. 2,356,254 discloses wax solvents which include aromatics, turpentine, chlorine-substituted aromatics, chlorine-substituted aliphatics, kerosene, carbon disulfide, carbon tetrachloride, gasoline, gas oil and petroleum extracts.
U.S. Pat. No. 2,753,939 discloses a solvent mixture composed of an aromatic hydrocarbon such as toluene and ether alcohol and dialkyl ether.
U.S. Pat. No. 3,241,614 discloses the cleaning of well drilling equipment using the mixture of two or more solvents and a surfactant. Solvents which are used include liquid hydrocarbons, liquid halogenated hydrocarbons, liquid amine substituted hydrocarbons and liquid oxygenated hydrocarbons including alcohols, ketones and acids. The liquid hydrocarbons may be aliphatic or aromatic in character. Specifically disclosed are solvents such as kerosene, gasoline, benzene, xylene, toluene, pentane, alkylene amines, dioxane, ketones, acetic acid, carbon disulfide and the like. It is disclosed that a mixture of two or more of the cited solvents may be used. Additionally, a surfactant is added to the solvent or solvent mixture. A preferred surfactant is an oxyethylene ether of an alkyl aryl compound, e.g., the oxyethylene ether of nonyl phenol.
U.S. Pat. No. 3,718,586 discloses a solvent for cleaning well bores which includes a liquified petroleum gas and a normally liquid aromatic hydrocarbon. It is disclosed that increased solvent properties are obtained by the addition of a liquid petroleum sulfonate as well as a surfactant and ethylene glycol.
The terms "paraffin" and "paraffin-like" as used throughout the specification refer to any material which is insoluble, sparingly soluble, or undispersible in crude oil under conditions of production. Thus, the paraffin deposit may contain high molecular weight aliphatic hydrocarbons, e.g., long chain alkanes and alkyl-substituted alkanes having at least about 20 carbon atoms, petroleum resins, asphaltic materials, aromatic hydrocarbons, mineral matter and the like. As will be understood by those skilled in the art, the composition of such deposits varies from one crude oil to another, from one field to another and from one oil well to another well in the same field.
In addition to solvent procedures, a variety of other procedures are being used to remove accumulations of paraffin materials. Most methods involve the use of the solvents described above or mechanical means to dissolve and wash out the accumulations. Over 50% of the cost of producing and marketing oil from producing wells is related to cleaning procedures acquired to dissolve and remove paraffin. The two most common techniques for affecting these cleaning procedures involve the use of mechanical scraping and hot oil flushing. The paraffin removed from well equipment by these techniques usually remains in a solid form or otherwise it quickly returns to a solid after treatment. This materials also tends to accumulate in flowlines and the like. Mechanical scraping, with specially designed instruments, is sometimes referred to as "knifing". Another physical process is that which involves passing a hot petroleum oil through the equipment in order to remove the paraffin. Unfortunately, the hot oil represents considerable cost in heating, pumping and the like and has a relatively low solvency for paraffin. Scraping is not applicable when removal of paraffin is required from pumps, valves and the like.